Heavy machinery, such as off-highway trucks, are commonly used in mining, heavy construction, quarrying, and other applications. Although such machines are traditionally directly driven via an internal combustion engine, the extensive fuel consumption and mechanical complexity of such systems has spurred wide-ranging exploration of alternative power systems.
One advance that has improved efficiency associated with the use of heavy machinery is the adoption of Alternating Current (AC) or electric drive systems. Electric drive systems for machines typically include a power circuit that selectively activates one or more drive motors at a desired torque. Each of the drive motors is connected to a wheel or other traction device that operates to propel the machine. An electric drive system includes a prime mover, for example, an internal combustion engine, that drives a generator. The generator produces electrical power that is often conditioned, and ultimately used to drive the motor. The motor transforms the electrical power back into mechanical power that drives the wheel and propels the vehicle. Electric drive systems typically require less maintenance and thus, have lower life cycle costs.
However, there are other faults associated with such machines that warrant attention in order to provide optimal machine operation. For example, the primary voltage supply in such systems is ideally maintained at a relatively constant level. However, variable loading and changing operating conditions can lead to fluctuations in the voltage supply. This is especially troublesome in systems where both a generator and one or more drive motors can impose a voltage on the supply link. For example, during retarding of such a machine, the drive motors act as generators and will increase the supply voltage to sometimes unacceptable levels unless these fluctuations can be managed and mitigated. This and other shortcomings in the state of the art are addressed by aspects of the disclosed principles.